Process for generating acid anhydrides

ABSTRACT

Provided is a method of producing an anhydride of an organic mono-acid comprising contacting an organic mono-acid and a thermally regenerable anhydride to produce the anhydride of the organic mono-acid, and either a diacid of the regenerable anhydride, a partially hydrolyzed regenerable anhydride, or both. In a particular example, acetic acid and glutaric anhydride can be reacted to form acetic anhydride.

CROSS-REFERENCE TO A RELATED APPLICATION

This patent application claims the benefit of U.S. Provisional PatentApplication No. 63/022,075, filed May 8, 2020, which is incorporated byreference.

BACKGROUND OF THE INVENTION

Anhydrides are useful, reactive species that are often used as waterscavengers or acylation agents in chemical processes. Directcondensation of acids to anhydrides is an energetically unfavorablereaction, particularly for monoacid species, so the synthesis of theseanhydrides typically is energy intensive, carried out at elevatedtemperatures and pressures, and/or is poorly selective in productformation.

Acetic anhydride is produced commercially by three routes: ketenereaction, carbonylation of methyl acetate, and direct oxidation ofacetaldehyde. The ketene route is the most widely practiced industrialacetic anhydride process and involves pyrolyzing acetic acid or acetoneto ketene at reduced pressure and very high temperature, then reactingthe ketene with acetic acid at near ambient temperature in a compressor(see, e.g., U.S. Pat. No. 3,111,548). The carbonylation process involvesesterification of acetic acid with methanol to form methyl acetate atmoderate temperature. The methyl acetate is then reacted with carbonmonoxide at elevated temperature and high pressure (see, e.g., U.S. Pat.No. 4,002,677). Water is also added to the reactor to control the ratioof acetic acid and acetic anhydride. While it is conducted at lowtemperature and pressure, the direct oxidation of acetaldehyde routesuffers from low selectivity (about 80 mol % versus greater than 90 mol% for the other routes) making it economically unattractive. Analogousversions of the above routes are known for producing other anhydrides,although one common technique is to use excess acetic anhydride toproduce other desired anhydrides.

Production of acetic anhydride from reacting acetic acid with a cyclicanhydride has been described in the literature (Haddadin et al., J.Pharm. Sci., 1975, 64(11), 1759-1765). However, these experiments relyon having a large excess of acetic acid present as well as a strong acidcatalyst (e.g., perchloric acid) to achieve <10% acetic anhydride(relative to acetic acid). As this equilibrium lies heavily on the sideof glutaric anhydride, one efficient and practiced industrial method forglutaric anhydride production involves treatment of glutaric acid andits derivatives with a slight excess of acetic anhydride to generateglutaric anhydride quantitatively (Cason, Org. Synth., 1958, 38, 52; andBesrat et al., J. Biol. Chem., 1969, 244(6), 1461-1467). In practicehowever, this reaction is presumed to be practically irreversible, noprocesses have described utilization of this reverse reaction togenerate acetic anhydride, and no methods utilizing low aceticacid/glutaric anhydride ratios have been described to date. Furthermore,the coupling of this type of non-thermally generable anhydrideproduction reaction with a thermally regenerable anhydride reaction(e.g., glutaric acid to glutaric anhydride and water) to create acontinuous process has not been described.

Thus, there remains a need for alternative syntheses for producinganhydrides that work under less harsh conditions while still maintaininga high degree of selectivity.

BRIEF SUMMARY OF THE INVENTION

The invention provides a method of producing an anhydride of an organicmono-acid comprising contacting an organic mono-acid and a thermallyregenerable anhydride to produce the anhydride of the organic mono-acidand either a diacid of the regenerable anhydride, a partially hydrolyzedregenerable anhydride, or both a diacid of the regenerable anhydride anda partially hydrolyzed regenerable anhydride.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 contains two different generalized schemes illustrating thetwo-step process of: 1) conversion of an organic mono-acid and aregenerable anhydride to the anhydride or mixed anhydride of the organicmono-acid and the hydrolyzed regenerable anhydride (transanhydridizationreaction) and 2) the regeneration of the regenerable anhydride with lossof water (anhydride regeneration reaction).

FIG. 2 is a series of reactions showing hydrolysis of an anhydride toform a partially hydrolyzed anhydride using, for example, polyphosphoricacid and pyromellitic anhydride.

FIG. 3 is a scheme illustrating an acetic acid feed (AcOH) feed and aglutaric anhydride feed to generate acetic anhydride (Ac₂O).

FIG. 4 is a reaction scheme illustrating acetic acid (organic mono-acid)reacting with glutaric anhydride (regenerable anhydride) to form aceticanhydride (anhydride of the organic mono-acid) and glutaric acid (diacidof the anhydride), which is subsequently dehydrated to reform glutaricanhydride (regenerable anhydride).

DETAILED DESCRIPTION OF THE INVENTION

The invention provides an anhydride synthesis that occurs at ambient ornear-ambient pressure and moderate temperatures (e.g., about 200° C. orlower). Moreover, the process does not require a catalyst to generateanhydride at high selectivity, although a catalyst can be added. Theprocess can use relatively inexpensive dehydrating agents, includingindustrial byproducts (e.g., glutaric anhydride) and/or low-costmaterials (e.g., polyphosphoric acid). As an added advantage, theinventive process does not require adding a third component (e.g.,water) to the system to control the acid/anhydride ratio as needed inthe standard carbonylation process. Rather, the residence time and/orrelative flow rates of the starting acid and regenerable anhydride canbe manipulated to adjust the ratio.

In particular, the invention provides a method of producing an anhydrideof an organic mono-acid comprising contacting an organic mono-acid and athermally regenerable anhydride to produce the anhydride of the organicmono-acid and either a diacid of the thermally regenerable anhydride, apartially hydrolyzed anhydride, or both a diacid of the anhydride and apartially hydrolyzed anhydride. This transanhydridization reaction isillustrated in FIG. 1 . Generation of a partially hydrolyzed anhydrideis shown in FIG. 2 . In general, a stream containing at least oneorganic mono-acid (“organic mono-acid” or “organic acid”) is reactedwith a stream containing at least one anhydride that is capable of beingregenerated (“thermally regenerable anhydride” or “regenerableanhydride”). The reaction yields a stream containing one or more desiredanhydrides and the acid form(s) of the regenerable anhydride(s), as wellas unreacted acid and unreacted, regenerable anhydride. The reaction canbe run to completion or to partial completion at various ratios of thereactants.

Following the reaction, the residual reactants and products areseparated into various streams in one or more steps. For example, themethod comprises a separation step comprising forming a first streamcomprising the anhydride of the organic mono-acid (desired product) andany unreacted organic mono-acid and forming a second stream comprisingthe diacid of the regenerable anhydride, partially hydrolyzed anhydride,and/or unreacted anhydride. In some embodiments, residual unreactedregenerable anhydride is extracted from its acid form to drive theregeneration reaction forward.

The separation steps described herein can use any suitable method ofphysical separation, including distillation (e.g., simple, molecular,evaporative, short path, batch, continuous, flash, steam, vacuum, lowtemperature, fractional, azeotropic, extractive, or a combinationthereof). In some embodiments and depending on the reactants, theseparation step is by either fractional distillation, azeotropicdistillation, and/or extractive distillation.

In an azeotropic distillation or other distillation with two or morecompounds with a close boiling point differential, typically a newcomponent (e.g., entrainer) is added to the azeotrope or otherwiseinseparable mixture. The new component serves to form two or moreimmiscible liquid phases that can be separated. In addition, a thirdcomponent such as a solid dehydrating agent can be added, e.g.,molecular sieves, silica gel, alumina, other thermally regenerable soliddrying agents, and combinations thereof.

Azeotropic distillation can be performed as homogenous azeotropicdistillation, heterogeneous azeotropic distillation, reactivedistillation, and salted distillation. In homogenous azeotropicdistillation, an entrainer is added that is miscible with the originalmixture. In heterogeneous azeotropic distillation, an entrainer is addedthat forms a heterogeneous azeotrope with one or more components in theoriginal mixture. In reactive distillation, an entrainer is added thatreacts with one or more components in the original mixture. Thenon-reacting component is produced as a distillate, and the entrainer isrecovered from the reverse reaction. Salted distillation is a type ofextractive distillation, in which relative volatility is altered by theaddition of salt as an entrainer.

In certain embodiments, the unreacted organic mono-acid is separatedfrom the anhydride of the organic mono-acid. If desired, the separated,unreacted organic mono-acid can be recycled for reuse as a startingmaterial. In some instances, a portion of the unreacted organicmono-acid is diverted to a vessel containing the second stream. In suchinstances, it is believed that the recycled organic mono-acid can act asan entrainer or azeotroping agent to remove water during regeneration ofthe regenerable anhydride.

The regenerable anhydride is regenerated by removing water from themulti-acid form of the regenerable anhydride. In any of the foregoingembodiments, to regenerate the anhydride the second stream can beoptionally heated in the presence or absence of a catalyst and subjectedto distillation (e.g., azeotropic distillation). Preferably, theregenerable anhydride is regenerated in a separate step from thereaction that generates the anhydride of the organic mono-acid. In somepreferred embodiments, the regenerated anhydride can be recycled forreuse as a starting material.

The reactants and products of the inventive method can be separatedand/or concentrated by a number of different unit operations. Thereaction and separation steps can be combined or coupled. Similarly, theseparation and regeneration steps can be combined or coupled. Unitoperations include, for example, distillation, extractive distillation,reactive distillation, extraction, reactive extraction, mixing-settling,pervaporation, membrane separation, evaporation, condensation, flashing,fractionation, electrotreatment, flotation, phase separation,coalescence, hydrocycloning, decanting, parametric pumping, sublimation,ion exchange, adsorption, absorption, and/or crystallization.

In the method, the anhydride starting material is any suitableregenerable anhydride. In some instances, the regenerable anhydride iscyclic or can form a cyclic structure. It has been observed that ananhydride with a cyclic structure or that can form a cyclic structurecan be more easily thermally regenerated. In some embodiments, thethermally regenerable anhydride is selected from a carboxylic acidanhydride, a sulfonic acid anhydride, a phosphinic acid anhydride, aphosphonic acid anhydride, a phosphoric acid anhydride, and a mixedanhydride. In some embodiments, the mixed anhydride contains acombination of different acid moieties. In some embodiments, the mixedanhydride has different backbone structures (e.g., a mixed anhydridecreated from the condensation of the organic mono-acid in the feed andanother acidic moiety). Preferably, at least a portion of the structureof the mixed anhydride is in cyclic form or capable of forming a cyclicstructure.

In general, the regenerable carboxylic acid anhydride can have a cyclicstructure of the formula R¹—C(O)—O—C(O)—R², in which R¹ and R² arelinked together to form an alkylene with 1 or 2 optional double bonds,arylene, or a mixed alkylene/arylene group. The mixed alkylene/arylenegroup can in some instances form dianhydride or trianhydride. Thealkylene with 1 or 2 optional double bonds, arylene, and mixedalkylene/arylene group is optionally substituted with one or moresubstituents (e.g., 1, 2, 3, 4, 5, 6, etc.) selected from alkyl(including alkylene), halo, alkoxy, trialkylsiloxy, nitro, aryl, andcarboxy-substituted phenyl. Examples of the carboxylic acid anhydrideinclude, e.g., tetrafluorosuccinic anhydride, maleic anhydride, itaconicanhydride, succinic anhydride, glutaric anhydride, 2,7-oxepanedione(adipic anhydride), azelaic anhydride, suberic anhydride, sebacicanhydride, 3-methylglutaric anhydride, methylsuccinic anhydride,3-(t-butyldimethylsilyloxy)glutaric anhydride,1,2-cyclohexanedicarboxylic anhydride, 1,3-cyclohexanedicarboxylicanhydride, camphoric anhydride, homophthalic anhydride, phthalicanhydride, isophthalic anhydride, trimellitic anhydride, pyromelliticdianhydride, mellitic trianhydride, and 3- or 4-fluorophthalicanhydride.

In general, the regenerable sulfonic acid anhydride has the formulaR³—S(O)₂—O—S(O)₂—R⁴, in which R³ and R⁴ are the same or different andeach is a C₁₋₁₂ alkyl group or aryl group (e.g., phenyl) or R³ and R⁴are linked together to form an alkylene, arylene, or mixedalkylene/arylene group. Each C₁₋₁₂ alkyl, aryl, alkylene, arylene, andmixed alkylene/arylene group is optionally substituted with one or moresubstituents (e.g., 1, 2, 3, 4, or 5) selected from alkyl, halo, alkoxy,trialkylsiloxy, nitro, and aryl. Examples of the sulfonic acid anhydrideinclude, e.g., methanesulfonic anhydride, 1,2-ethane disulfonicanhydride, nonafluorobutanesulfonic anhydride, and p-toluenesulfonicanhydride.

A regenerable phosphinic acid anhydride has the formulaR⁵—P(O)(R⁶)—O—P(O)(R⁷)—R⁸ in which R⁵, R⁶, R⁷, and R⁸ are the same ordifferent and each is H, a C₁₋₁₂ alkyl group, or aryl group (e.g.,phenyl) or R⁵ and R⁸ are linked together to form an alkylene, arylene,or mixed alkylene/arylene group. Each C₁₋₁₂ alkyl, aryl, alkylene,arylene, and mixed alkylene/arylene group is optionally substituted withone or more substituents (e.g., 1, 2, 3, 4, or 5) selected from alkyl,halo, alkoxy, trialkylsiloxy, nitro, and aryl. Examples of thephosphinic acid anhydride include, e.g.,propane-1,3-bis(methylphosphinic acid) anhydride,butane-1,4-bis(methylphosphinic acid) anhydride,hexane-1,6-bis(methylphosphinic acid) anhydride anddecane-(1,10-bismethylphosphinic acid) anhydride.

A regenerable phosphonic acid anhydride has the formulaR⁹—P(O)(OH)—O—P(O)(OH)—R¹⁰, R⁹—P(O)(OH)-13[O—P(O)(R¹⁰)]_(n)—O—P(O)(OH)—R¹¹, or

in which R⁹, R¹⁰, and ^(Ru) are the same or different and each is aC₁₋₁₂ alkyl group or aryl group (e.g., phenyl) or R⁹ and R¹⁰ are linkedtogether to form an alkylene, arylene, or mixed alkylene/arylene group.Each C₁₋₁₂ alkyl, aryl, alkylene, arylene, and mixed alkylene/arylenegroup is optionally substituted with one or more substituents (e.g., 1,2, 3, 4, or 5) selected from alkyl, halo, alkoxy, trialkylsiloxy, nitro,and aryl. Examples of the phosphonic acid anhydride include, e.g.,propane-phosphonic acid anhydride, butane-phosphonic acid anhydride,hexane-phosphonic acid anhydride, octane-phosphonic acid anhydride,decane-phosphonic acid anhydride, methane-pyrophosphonic acid anhydride,and propane-pyrophosphonic acid anhydride.

A regenerable phosphoric acid anhydride includes, for example,phosphorus pentoxide, pyrophosphoric acid, trimetaphosphoric acid,polyphosphates, cyclic polyphosphosphates, and polyphosphoric acid.

In some embodiments, the regenerable anhydride forms a polymericstructure. Typically, polymeric structures form with alkyene chainslonger than 5 carbons (e.g., C6, C7, C8, C9, C10, etc.). It is believedthat a polymeric structure forms when the terminus of one molecule bondsto the terminus of a second molecule and so on. A diacid that forms apolyanhydride can be of the formulaHO₂C—(CH₂)_(m)—C(O)—O—C(O)—(CH₂)_(n),—CO₂H, in which m and n are thesame or different and each is an integer from 6 to 12 (i.e., 6, 7, 8, 9,10, 11, or 12). In some embodiments, the polyanhydride can be of theformula:

in which R¹² is C₆₋₁₂ alkylene that optionally contains one or moredouble bonds, arylene, or a mixture thereof. The alkylene and arylenecan be substituted as described herein. The subscript “p” is the numberof repeat units and is an integer of at least 2 (e.g., 5 or more, 10 ormore, 15 or more, etc.). Examples of the diacid anhydride that can forma polyanhydride include, e.g., adipic anhydride, azelaic anhydride,suberic anhydride, sebacic anhydride, decane anhydride, dodecanedioicanhydride, 1,6-bis(p-carboxyphenoxy)hexane anhydride,1,3-bis(p-carboxyphenoxy)propane anhydride, p-carboxyphenoxymethaneanhydride, p-carboxyphenoxypropane anhydride, p-carboxyphenoxyvalericanhydride, p-carboxyphenoxyacetic anhydride, p-carboxyphenoxy octanoicanhydride, phenylenedipropionic anhydride, and combinations thereof. Thepolymeric anhydride can also be mixed in that two different acids arecondensed, such as sebacid acid copolymerized with1,3-bis(p-carboxyphenoxy)propane or 1,6-bis(p-carboxyphenoxy)hexane.

In certain instances, the regenerable anhydride is a mixture ofanhydrides that are in cyclic form, capable of forming a cyclicstructure, and/or polymeric form.

The regenerable anhydride can also be a mixed anhydride, which includesdifferent organic groups of a single type of anhydride (e.g., benzoicacid-trifluoroacetic acid anhydride) and an anhydride of both acarboxylic acid and a sulfonic acid (e.g., ortho/meta/para-sulfobenzoicanhydride, including mixtures thereof), a carboxylic acid and aphosphoric acid, or a sulfonic acid and a phosphoric acid. In someinstances, a mixed anhydride is created from the condensation of theorganic mono-acid and another acidic moiety present in the reaction.

In preferred embodiments, the regenerable anhydride is succinicanhydride, glutaric anhydride, nitrophthalic anhydride, homophthalicanhydride, 1,2-ethane disulfonic acid anhydride, polyphosphoric acid,pyromellitic anhydride, propanephosphonic anhydride, ortho-sulfobenzoicanhydride, mixed benzoic acid-trifluoroacetic acid anhydride, or anycombination thereof. More preferably, the anhydride is glutaricanhydride.

The regenerable anhydride can be added to the reaction in any suitablemanner.

The organic mono-acid is a carboxylic acid, a sulfonic acid, a sulfinicacid, a phosphonic acid, or a phosphinic acid. In general, thecarboxylic acid is of the formula R—C(O)OH; the sulfonic acid is of theformula R—S(O)₂OH; the sulfinic acid is of the formula R—S(O)OH; thephosphonic acid is of the formula R—P(O)(OH)₂; and the phosphinic acidis of the formula R—P(R′)(O)OH. In any of the foregoing formulas, R isC₁₋₁₈ alkyl or aryl. R′ is H, C₁₋₁₈ alkyl, or aryl. The C₁₋₁₈ alkyl andaryl groups for R and R′ can be optionally substituted with one or moresubstituents (e.g., 1, 2, 3, 4, 5, 6, etc.) selected from alkyl, halo,alkoxy, trialkylsiloxy, nitro, and aryl.

In some instances, the organic mono-acid is a C₁₋₁₈ monocarboxylic acid,a halo-substituted C₁₋₁₈ monocarboxylic acid (e.g., chloroacetic acid ortrifluoroacetic acid), an aryl-containing acid (e.g., benzoic acid orcinnamic acid), methanesulfonic acid, or a combination thereof.

In some instances, the organic mono-acid is a C₁₋₁₈ monocarboxylic acidsuch as, e.g., formic acid, acetic acid, propionic acid, butanoic acid(butyric acid), isobutyric acid, pentanoic acid (valeric acid), hexanoicacid (caproic acid), heptanoic acid, octanoic acid (caprylic acid),nonanoic acid (pelargonic acid), decanoic acid (capric acid), undecanoicacid (undecylic acid), dodecanoic acid (lauric acid), tridecanoic acid(tridecylic acid), tetradecanoic acid (myristic acid), pentadecanoicacid (pentadecylic acid), hexadecanoic acid (palmitic acid),heptadecanoic acid (margaric acid), octadecanoic acid (stearic acid), ora combination thereof. In a preferred embodiment, the organic mono-acidis acetic acid.

If desired, the organic mono-acid can be added in the form of a salt.While not wishing to be bound by any theory, it is believed that a saltfacilitates generation of non-volatile mixed anhydride intermediatesthat are more kinetically favorable for forming the desired anhydrideproduct from the organic mono-acid (e.g., monocarboxylic acid) than theanhydride (e.g., cyclic anhydride) alone. The organic mono-acid can be,for example, a salt of an alkali metal (e.g., Group 1 cations, such aslithium, sodium, or potassium), an alkaline earth metal (e.g., Group 2cations, such as calcium, magnesium, and barium), a transition metal(e.g., Group 3-12 cations, such as Fe(II), Zn(II), Cu(I), Cu(II),Cr(II), Al(III), Mn(II), or Ni(II)), or ammonium. In any of theforegoing formulas of the organic mono-acid, one or more hydrogens canbe replaced with a cation (X⁺), such as R—C(O)—O⁻X⁺. Examples of a saltof an organic mono-acid include, e.g., lithium acetate and potassiumisobutyrate.

The organic mono-acid can be present in the reactor and/or added to thereaction in a single stage or over multiple stages (e.g., 2 or morestages, 3 or more stages, 4 or more stages, 5 or more stages, 6 or more,etc.). Additionally, the organic mono-acid can be added in an amountthat is sub-stoichiometric to, stoichiometric to, or in excess of theregenerable anhydride. In certain embodiments, the organic mono-acid ispresent in the reactor in an amount that is in excess of the regenerableanhydride. In such scenarios, the ratio of organic mono-acid toregenerable anhydride ranges from 1:1 to 10:1 or is 1:1 or more (e.g.,2:1 or more, 3:1 or more, 4:1 or more, 5:1 or more, 6:1 or more, 7:1 ormore, 8:1 or more, or 9:1 or more) and/or 10:1 or less (e.g., 9:1 orless, 8:1 or less, 7:1 or less, 6:1 or less, 5:1 or less, 4:1 or less,3:1 or less, or 2:1 or less). Any two of the foregoing endpoints can beused to define a close-ended range, or a single endpoint can be used todefine an open-ended range.

In any of the embodiments above, the term “alkyl” implies astraight-chain or branched alkyl substituent containing from, forexample, from about 1 to about 18 carbon atoms, e.g., from about 1 toabout 14 carbon atoms, from about 1 to about 12 carbon atoms, from about1 to about 10 carbon atoms, from about 1 to about 8 carbon atoms, fromabout 1 to about 6 carbon atoms, or from about 1 to about 4 carbonatoms. Examples of alkyl group include methyl, ethyl, n-propyl,isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl,isopentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-dodecyl, andthe like. The alkyl can be substituted or unsubstituted, as describedherein.

The term “alkylene” refers to a divalent alkyl group, such as methylenyl(—CH₂—), ethylene (—CH₂CH₂—), propylene (—CH₂CH₂CH₂—), etc., in whichthe alkyl group is as described above. The alkylene can optionallyinclude 1 or 2 double bonds, such as (—CH═CH—), (—CH═CHCH₂—), or(—CH₂CH═CH—). Preferably, the alkylene contains from about 1 to about 6carbon atoms, from about 1 to about 4 carbon atoms, or from about 1 toabout 3 carbon atoms. The alkylene can be substituted as describedherein.

In any of the embodiments above, the term “aryl” refers to a mono, bi,or tricyclic carbocyclic ring system having one, two, or three aromaticrings, for example, phenyl, naphthyl, anthracenyl, or biphenyl. The term“aryl” refers to an unsubstituted or substituted aromatic carbocyclicmoiety, as commonly understood in the art, and includes monocyclic andpolycyclic aromatics such as, for example, phenyl, biphenyl, naphthyl,anthracenyl, pyrenyl, and the like. Preferably, the aryl is phenyl. Anaryl moiety generally contains from, for example, 6 to 30 carbon atoms,from 6 to 18 carbon atoms, from 6 to 14 carbon atoms, or from 6 to 10carbon atoms. It is understood that the term aryl includes carbocyclicmoieties that are planar and comprise 4n+2π electrons, according toHückel's Rule, wherein n=1, 2, or 3. The aryl can be substituted orunsubstituted, as described herein.

The term “arylene” refers to a divalent aryl group, such as divalentphenylene, etc., in which the aryl group is as described above. Thearylene can be substituted as described herein.

In any of the embodiments above, the term “halo” refers to a halogenmoiety selected from fluoro, chloro, bromo, and iodo.

In any of the embodiments above, the term “alkoxy” embrace a linear orbranched alkyl group that is attached to a divalent oxygen. The alkylgroup is the same as described herein.

The term “at least one” means 1 or more, 2 or more, 3 or more, or 4 ormore, including 1, 2, 3, 4, etc.

In any of the foregoing embodiments, the method can further comprise asuitable solvent. One purpose of a solvent may be to increase the rateof anhydride generation of the reaction by manipulating the dielectricconstant and/or solvation properties of the mixture. Without wishing tobe bound by theory, it is believed that running the reaction in a highdielectric solvent, such as sulfolane or dimethylsulfoxide (DMSO), couldallow for more efficient reactions with organic mono-acids, such aspolyphosphoric acid and low dielectric carboxylic acids. Another purposeof the solvent may be to act as an entrainer or azeotroping agent tofacilitate the separation of compounds in the system, particularly theproduct from the starting material. A temperature- or pressure-swingdistillation system can be used to facilitate further separation ofeither bottoms, distillate, or both. The solvent can be, for example,can be protic or aprotic and preferably has a dielectric constant (ε) isthat is 15 or more (e.g., ε is 20 or more, 25 or more, 30 or more, 35 ormore, 40 or more, etc.). The higher the dielectric constant, the higherthe polarity of the solvent. Examples of suitable solvents includeacetone, acetonitrile, N,N-dimethylacetamide, N,N-dimethylformamide(DMF), formamide, hexamethylphosphoramide, dimethylsulfoxide (DMSO),sulfolane, methanol, ethanol, ispropanol, nitrobenzene, nitromethane,cyclohexanone, methyl ethyl ketone, methyl cyclohexane, toluene,m-xylene, o-xylene, p-xylene, and any combination thereof. A preferredsolvent comprises DMSO, sulfolane, or a combination thereof. In someembodiments, a solvent is not used.

While typically not necessary, one or more catalysts can be used. Insome embodiments of the inventive method, a catalyst can be used tofacilitate the regeneration of the anhydride (e.g., cyclic anhydride),increase the rate of product generation, or both. A suitable catalystcan be homogeneous, insoluble but mobile (e.g., a slurry), orheterogeneous. Examples of catalysts include perchloric acid, magnesiumchloride, an ion exchange resin (e.g., a macro reticular (macroporous)polystyrene based ion exchange resin with strongly acidic sulfonicgroups, such as AMBERLYST™), a perfluorinated resin (e.g., a sulfonatedtetrafluoroethylene-based fluoropolymer-copolymer, such as NAFION™), anda combination thereof.

The transanhydridization reaction (FIG. 2 ) can be run at any suitabletemperature. In general, the transanhydridization reaction temperatureis moderate, such as a 200° C. or below, including 180° C. or below,160° C. or below, 150° C. or below, 145° C. or below, 140° C. or below,135° C. or below, 130° C. or below, 125° C. or below, 120° C. or below,115° C. or below, 110° C. or below, 105° C. or below, 100° C. or below,95° C. or below, 90° C. or below, 85° C. or below, 80° C. or below, 75°C. or below, 70° C. or below, 65° C. or below, 60° C. or below, 55° C.or below, or 50° C. or below. Typically, the transanhydridizationreaction temperature is performed at 45° C. or more (e.g., 50° C. ormore, 60° C. or more, 70° C. or more, 80° C. or more, 90° C. or more,100° C. or more, 110° C. or more, 120° C. or more, 130° C. or more, or140° C. or more). Any two of the foregoing endpoints can be used todefine a close-ended range, or a single endpoint can be used to definean open-ended range. In some preferred embodiments, the reactiontemperature is about 170° C. or below, more preferably 150° C. or below,120° C. or below, 115° C. or below, 110° C. or below, or 80° C. orbelow.

The transanhydridization reaction can be run under any suitable pressureand typically is run at ambient pressure (e.g., atmospheric pressure at1 atm) or near-ambient pressure (e.g., 1 atm±10%, 1 atm±5%, 1 atm±2%, or1 atm±1%). In some embodiments, the transanhydridization reaction is rununder slight pressure, such as 15 atm or less (e.g., 10 atm or less, 8atm or less, 6 atm or less, 5 atm or less, 4 atm or less, 3 atm or less,or 2 atm or less). In such embodiments, the reaction pressure typicallywill be at 1 atm or more (e.g., 2 atm or more, 3 atm or more, 4 atm ormore, 5 atm or more, 6 atm or more, 7 atm or more, 8 atm or more, 9 atmor more, 10 atm or more, or 12 atm or more). For the separation step(e.g., the pressure in a stripping column), the pressure typically islower to help prevent the reverse reaction from proceeding, such as 0.05atm or more (e.g., 0.1 atm or more, 0.2 atm or more, 0.5 atm or more,0.8 atm or more, 1 atm or more and/or 5 atm or less, 2 atm or less, 1atm or less, 0.8 atm or less, 0.5 atm or less, 0.2 atm or less, or 0.1atm or less). Any two of the foregoing endpoints can be used to define aclose-ended range, or a single endpoint can be used to define anopen-ended range.

The transanhydridization reaction be can run for any suitable length oftime. The reaction time can be 0.01 hours or more (e.g., 0.05 hours ormore, 0.1 hours or more, 0.15 hours or more, 0.02 hours or more, 0.25hours or more 0.5 hours or more, 0.75 hours or more, 1 hour or more, 1.5hours or more, 2 hours or more, 3 hours or more, 4 hours or more, or 5hours or more). Typically the reaction run will be complete in 4 days orless (e.g., 3.5 days or less, 3 days or less, 2.5 days or less, 2 daysor less, 1 day or less, 20 hours or less, 15 hours or less, 10 hours orless, 8 hours or less, 6 hours or less, 5 hours or less, 4 hours orless, 3 hours or less, 2 hours or less, or 1 hour or less). Any two ofthe foregoing endpoints can be used to define a close-ended range, or asingle endpoint can be used to define an open-ended range.

The anhydride regeneration reaction (FIG. 2 ) can be run at any suitabletemperature that regenerates the anhydride (e.g., 350° C. or below, 325°C. or below, 300° C. or below, 275° C. or below, 250° C. or below, 225°C. or below, 200° C. or below, 175° C. or below, 150° C. or below, 125°C. or below, 100° C. or below, 90° C. or below, 85° C. or below, 80° C.or below, 75° C. or below, 70° C. or below, 65° C. or below, 60° C. orbelow, 55° C. or below, or 50° C. or below). Typically, the anhydrideregeneration reaction temperature is performed at 30° C. or more (e.g.,40° C. or more, 50° C. or more, 60° C. or more, 70° C. or more, 75° C.or more, 80° C. or more, 85° C. or more, 90° C. or more, 100° C. ormore, 110° C. or more, 115° C. or more, 125° C. or more, 130° C. ormore, 135° C. or more, 140° C. or more, 145° C. or more, 150° C. ormore, 175° C. or more, or 200° C. or more). Any two of the foregoingendpoints can be used to define a close-ended range, or a singleendpoint can be used to define an open-ended range.

The anhydride regeneration reaction can be run under any suitablepressure and typically is run at atmospheric pressure (about 1 atm) orreduced pressure.

The method has a high selectivity in that minimal byproducts aredetected beyond the expected products. For example, the term “highselectivity” means that 85 mol % or more (e.g. 87 mol % or more, 89 mol% or more, 90 mol % or more, 92 mol % or more, 94 mol % or more, 95 mol% or more, 96 mol % or more, 97 mol % or more, 98 mol % or more, or 99mol % or more) in any conversion observed to form the desiredproduct(s).

In a preferred example of the inventive method, the anhydride isglutaric anhydride, the organic mono-acid is acetic acid, and theanhydride of the monocarboxylic acid is acetic anhydride.

The inventive method can be used to generate anhydrides for use in asubsequent processing step on-site (e.g., cellulose acetatemanufacturing) or to generate anhydrides in a solvent for shipment. Theprocess can be collocated with other processes, such as utilizing aglutaric acid byproduct steam of adipic acid manufacturing to generate amore valuable acetic anhydride product stream. The process can betightly integrated with other processes. For example, in the productionof cellulose acetate, the acetic acid byproduct stream could beconverted to acetic anhydride raw material, with consideration for heatintegration of the unit operations.

In any of the methods described herein, the intrinsic capital intensityof the process in 2020 USD is less than $5,000 (e.g., less than $4,500,less than $4,000, less than $3,500, less than $3,000, less than $2,500,less than $2,000, less than $1,500, or less than $1,000) per ton ofinstalled annual capacity. In some embodiments, the intrinsic capitalintensity of the process in 2020 USD is $1,000 or more (e.g., $1,000 ormore, $1,500 or more, $2,000 or more, $2,500 or more, $3,000 or more,$3,500 or more, $4,000 or more, or $4,500 or more) per ton of installedannual capacity. Any two of the foregoing endpoints can be used todefine a close-ended range, or a single endpoint can be used to definean open-ended range. The installed annual capacity is for a plant sizewith a capacity of less than 36 thousand metric tons per year (kmta)(e.g., less than 34 kmta, less than 30 kmta, less than 30 kmta, lessthan 28 kmta, less than 25 kmta, less than 22 kmta, less than 20 kmta,less than 18 kmta, less than 16 kmta, less than 15 kmta, less than 14kmta, less than 12 kmta, less than 10 kmta, less than 8 kmta, less than6 kmta, or less than 5 kmta).

In any of the methods described herein, the intrinsic capital intensityof the overall process is more than 5% lower than the intrinsic capitalintensity of a ketene-based acetic acid to acetic anhydride process atthe same plant size. For example, the intrinsic capital intensity of theoverall process preferably is more than 10% lower (e.g., more than 15%lower, more than 20% lower, more than 25% lower, more than 30% lower,more than 35% lower, more than 40% lower) than the intrinsic capitalintensity of a ketene-based acetic acid to acetic anhydride process atthe same plant size. In any of these embodiments, the plant size is lessthan 50 kmta capacity (e.g., less than 45 kmta capacity, less than 40kmta capacity, less than 35 kmta capacity, less than 30 kmta capacity,less than 25 kmta capacity, less than 20 kmta capacity, less than 15kmta capacity, less than 10 kmta capacity, or less than 5 kmtacapacity).

In any of the methods described herein, the intrinsic capital intensityof the ISBL (inside battery limits) equipment of the overall process ismore than 5% lower than the intrinsic capital intensity of the ISBLequipment of a ketene-based acetic acid to acetic anhydride process atthe same plant size. For example, the intrinsic capital intensity of theISBL equipment of the overall process preferably is more than 10% lower(e.g., more than 15% lower, more than 20% lower, more than 25% lower,more than 30% lower, more than 35% lower, more than 40% lower) than theintrinsic capital intensity of the ISBL equipment of a ketene-basedacetic acid to acetic anhydride process at the same plant size. In anyof these embodiments, the plant size is less than 50 kmta capacity(e.g., less than 45 kmta capacity, less than 40 kmta capacity, less than35 kmta capacity, less than 30 kmta capacity, less than 25 kmtacapacity, less than 20 kmta capacity, less than 15 kmta capacity, lessthan 10 kmta capacity, or less than 5 kmta capacity).

In any of the methods described herein, the intrinsic capital intensityof the ISBL (inside battery limits) and OSBL (outside battery limits)equipment of the overall process is more than 5% lower than theintrinsic capital intensity of the ISBL and OSBL equipment of aketene-based acetic acid to acetic anhydride process at the same plantsize. For example, the intrinsic capital intensity of the ISBL and OSBLequipment of the overall process preferably is more than 10% lower(e.g., more than 15% lower, more than 20% lower, more than 25% lower,more than 30% lower, more than 35% lower, more than 40% lower) than theintrinsic capital intensity of the ISBL and OSBL equipment of aketene-based acetic acid to acetic anhydride process at the same plantsize. In any of these embodiments, the plant size is less than 50 kmtacapacity (e.g., less than 45 kmta capacity, less than 40 kmta capacity,less than 35 kmta capacity, less than 30 kmta capacity, less than 25kmta capacity, less than 20 kmta capacity, less than 15 kmta capacity,less than 10 kmta capacity, or less than 5 kmta capacity).

As used herein, the term “intrinsic capital intensity” refers to thecapital cost in dollars, divided by installed annual capacity of achemical plant performing a specific process or chemical transformation.The intrinsic capital intensity for a process can be defined as that ofthe ISBL (inside battery limits) equipment or the ISBL plus OSBL(outside battery limits) equipment (either on an installed cost basis),or the entire plant project cost.

The invention is further illustrated by the following aspects.

Aspect (1) A method of producing an anhydride of an organic mono-acidcomprising contacting an organic mono-acid and a thermally regenerableanhydride to produce the anhydride of the organic mono-acid and a diacidof the regenerable anhydride or a partially hydrolyzed anhydride.

Aspect (2) The method of aspect (1), wherein the anhydride of theorganic mono-acid and the diacid of the regenerable anhydride orpartially hydrolyzed anhydride are separated.

Aspect (3) The method of aspect (2), wherein the separation stepcomprises forming a first stream comprising the anhydride of the organicmono-acid and unreacted organic mono-acid and a second stream comprisingthe diacid of the regenerable anhydride or partially hydrolyzedanhydride and unreacted anhydride.

Aspect (4) The method of anyone of aspects (1)-(3), wherein theseparation step is by distillation.

Aspect (5) The method of aspect (3) or (4), wherein the unreactedorganic mono-acid is separated from the anhydride of the organicmono-acid.

Aspect (6) The method of aspect (5), wherein the separated, unreactedorganic mono-acid is recycled.

Aspect (7) The method of any one of aspect (3)-(6), wherein the secondstream is heated to regenerate the regenerable anhydride.

Aspect (8) The method of aspect (7), wherein azeotropic distillation isused to regenerate the regenerable anhydride.

Aspect (9) The method of aspect (7) or aspect (8), wherein theregenerable anhydride is recycled.

Aspect (10) The method of any one of aspects (1)-(9), wherein theregenerable anhydride is cyclic or can form a cyclic structure.

Aspect (11) The method of any one of aspects (1)-(10), wherein theregenerable anhydride is selected from a carboxylic acid anhydride, asulfonic acid anhydride, a phosphinic acid anhydride, a phosphonic acidanhydride, and a mixed anhydride containing a combination of differentacid moieties or different backbone structures.

Aspect (12) The method of any one of aspects (1)-(11), wherein theregenerable anhydride is selected from succinic anhydride, glutaricanhydride, nitrophthalic anhydride, homophthalic anhydride, 1,2-ethanedisulfonic acid, polyphosphoric acid, ortho-sulfobenzoic anhydride, andmixed benzoic acid-trifluoroacetic acid anhydride.

Aspect (13) The method of any one of aspects (1)-(12), wherein theregenerable anhydride is glutaric anhydride.

Aspect (14) The method of any one of aspect (1)-(13), wherein theorganic mono-acid is a carboxylic acid, a sulfonic acid, a sulfinicacid, a phosphonic acid, or a phosphinic acid.

Aspect (15) The method of aspect (14), wherein the carboxylic acid is aC₁₋₁₂ monocarboxylic acid.

Aspect (16) The method of aspect (15), wherein the C₁₋₁₂ monocarboxylicacid is selected from formic acid, acetic acid, propionic acid, butanoicacid (butyric acid), isobutyric acid, pentanoic acid (valeric acid),hexanoic acid (caproic acid), heptanoic acid, octanoic acid (caprylicacid), decanoic acid (capric acid), and dodecanoic acid.

Aspect (17) The method of any one of aspects (1)-(16), wherein theorganic mono-acid is acetic acid.

Aspect (18) The method of any one of aspects (1)-(17), wherein theanhydride of the monocarboxylic acid is acetic anhydride.

Aspect (19) The method of any one of aspects (1)-(18), wherein theorganic mono-acid is added in excess of the anhydride.

Aspect (20) The method of any one of aspects (1)-(19), wherein theorganic mono-acid is added over multiple stages.

Aspect (21) The method of any one of aspects (1)-(20) further comprisingadding a salt of the organic mono-acid.

Aspect (22) The method of any one of aspects (1)-(21) further comprisinga solvent.

Aspect (23) The method of any one of aspects (1)-(22) further comprisinga catalyst.

Aspect (24) The method of any one of aspects (3)-(23), wherein a portionof the monocarboxylic acid is diverted to a vessel containing the secondstream.

The following examples further illustrate the invention but, of course,should not be construed as in any way limiting its scope.

EXAMPLE 1

This example demonstrates a general method of producing an anhydride ofan organic mono-acid by reacting an organic mono-acid and a regenerableanhydride.

A low-boiling monocarboxylic acid (such as acetic acid, propionic acid,or isobutyric acid) is fed to a reactor and reacted with ahigher-boiling regenerable cyclic anhydride (such as succinic anhydride,glutaric anhydride, 1,2-ethanedisulfonic acid anhydride, orortho-sulfobenzoic anhydride) to generate the anhydride of themonocarboxylic acid and the diacid form of the regenerable cyclicanhydride.

The mixture of products and starting material is separated in a seriesof flash stages or distillations to yield a first stream principallycomprised of the generated anhydride and residual monocarboxylic acidand a second stream principally comprised of the residual regenerablecyclic anhydride and the generated diacid of the regenerable cyclicanhydride. The stream containing the anhydride product is then furtherconcentrated in the anhydride product through partial condensation,flash, or distillation, and most of the residual monocarboxylic acid isrecycled to the initial reactor. The stream containing residualregenerable cyclic anhydride is regenerated thermally, generated wateris removed, and the regenerable cyclic anhydride is recycled to thereactor. FIG. 3 is a scheme illustrating an acetic acid feed (AcOH) feedand a glutaric anhydride feed to generate acetic anhydride (Ac₂O). FIG.4 shows the reaction scheme for this process. Acetic acid (organicmono-acid) is reacted with glutaric anhydride(regenerable anhydride) toform acetic anhydride (anhydride of the organic mono-acid) and glutaricacid (diacid of the regenerable anhydride). The glutaric acid isdehydrated to regenerate the glutaric anhydride (regenerable anhydride).

EXAMPLE 2

This example demonstrates a method of producing various anhydrides usinga regenerable anhydride and an organic mono-acid in an embodiment of theinvention.

Following the procedure set forth in Example 1, solutions of regenerableanhydride in organic mono-acid were heated at either 50° C. or 100° C.for the indicated time in a batch reactor. No solvents or catalysts wereused. The products were analyzed by nuclear magnetic resonance (NMR)spectra. No byproducts were detected by NMR, suggesting very highselectivity. The results of these experiments are set forth in Table 1.

TABLE 1 Organic Tem- mono-acid Regenerable pera- Acid (concentrationAnhydride ture Time Conversion (M)) (concentration (M)) (° C.) (hr) (mol%) Acetic Acid Glutaric Anhydride  50 0.5  2.8 (16.0) (1.0) Acetic AcidGlutaric Anhydride  50 0.5  4.3 (14.4) (2.0) Acetic Acid GlutaricAnhydride  50 0.5  6.7 (11.3) (4.0) Acetic Acid Glutaric Anhydride 1000.25  8.0 (9.9) (5.0) Acetic Acid Glutaric Anhydride 100 0.5 12.6 (9.9)(5.0) Acetic Acid Polyphosphoric Acid* 100 0.5  9.1 (9.1) (4.5) AceticAcid o-Sulfobenzoic Acid 100 0.5  1.8 (14.9) Anhydride (1) Acetic Acido-Sulfobenzoic Acid 100 0.5  5.2 (7.8) Anhydride (2) Acetic Acido-Sulfobenzoic Acid 100 0.5  8.0 (7.8) Anhydride (4.8) Propanoic AcidGlutaric Anhydride 100 0.5 10.1 (7.6) (4.9) *Molarity based on c.a. 84wt % P₂O₅ equivalent as anhydride equivalent, balance H₃PO₄.

EXAMPLE 3

This example demonstrates a method of producing various anhydrides usinga regenerable anhydride and an organic mono-acid under various reactionconditions in an embodiment of the invention.

The solids and/or liquids were added to 2-dram vials withpolytetrafluoroethylene (PTFE) caps or 2-5 ml microwave vials with crimpcaps, and each vial was equipped with a stir bar. In some trials. acorresponding co-solvent was added to the corresponding vial and sealed.The sealed vials were placed into a preheated (75-150° C.) aluminum pieblock, and the reactions were stirred at 800 rpm for 1 hr. The vialswere removed from the heat and cooled on a room temperature aluminum pieblock. If the reaction mixture was homogeneous at room temperature, adichloromethane (DCM) standard was added, and an NMR sample wasprepared. If the reaction mixture was a solid at room temperature, anappropriate amount of DMSO or DMF was added to the reaction mixture todissolve the solids. A DCM standard was added to the reaction mixtureand an NMR sample was prepared. The solutions were added to NMR tubescontaining a capillary containing C₆D₆ and NMRs were taken with longrelaxation delays to ensure quantitative NMRs. The reaction conditionsare set forth in Table 2, and the products are set forth in Table 3.

TABLE 2 Acid Anhydride Co-solvent [CS] [HX] [X′₂O] Entry T (° C.) (HX)(X′₂O) (CS) (M) (M) (M) 1 75 Acetic Glutaric N/A N/A 8.75 4.38 2 75Propionic Glutaric N/A N/A 8.75 4.38 3 75 Chloroacetic Glutaric N/A N/A7.87 3.94 4 110 Acetic Glutaric N/A N/A 8.75 4.38 5 110 PropionicGlutaric N/A N/A 8.75 4.38 6 110 Chloroacetic Glutaric N/A N/A 7.87 3.947 110 Benzoic Glutaric N/A N/A 6.30 3.15 8 110 Cinnamic Glutaric N/A N/A5.25 2.63 9 150 Acetic Glutaric N/A N/A 8.75 4.38 10 150 PropionicGlutaric N/A N/A 8.75 4.38 11 150 Chloroacetic Glutaric N/A N/A 7.873.94 12 150 Benzoic Glutaric N/A N/A 6.30 3.15 13 150 Cinnamic GlutaricN/A N/A 5.25 2.63 14 110 Acetic Succinic N/A N/A 8.75 4.38 15 150 AceticSuccinic N/A N/A 8.75 4.38 16 150 Acetic Pyromellitic N/A N/A 8.75 2.1917 150 Acetic Glutaric Cyclohexanone 4.82 4.38 2.19 18 150 AceticGlutaric Cyclohexanone 6.43 2.92 1.46 19 150 Acetic GlutaricCyclohexanone 7.72 1.75 0.88 20 150 Acetic Glutaric m-xylene 4.09 4.382.19 21 150 Acetic Glutaric m-xylene 5.45 2.92 1.46 22 150 AceticGlutaric m-xylene 6.54 1.75 0.88 23 150 Myristic Glutaric DMF 6.46 2.131.06 24 150 Benzoic Glutaric DMF 6.46 3.15 1.58 25 150 Cinnamic GlutaricDMF 6.46 3.15 1.58 26 75 Acetic Sulfobenzoic N/A N/A 8.75 4.38 27 110Acetic Sulfobenzoic N/A N/A 8.75 4.38 28 150 Acetic Sulfobenzoic N/A N/A8.75 4.38 29 110 Myristic Glutaric N/A N/A 4.25 2.13 30 110Trifluoroacetic Glutaric N/A N/A 10.00 5.00 31 110 MethanesulfonicGlutaric N/A N/A 9.63 4.81 32 110 Acetic Propane N/A N/A 8.75 1.46phosphonic 33 75 Trifluoroacetic Glutaric N/A N/A 10.00 5.00 34 75Methanesulfonic Glutaric N/A N/A 9.63 4.81 35 75 Acetic Propane N/A N/A8.75 1.46 phosphonic 36 110 Trifluoroacetic Glutaric N/A N/A 5.00 5.0037 110 Trifluoroacetic Glutaric N/A N/A 10.00 2.50 38 110Methanesulfonic Glutaric N/A N/A 6.02 6.02 39 110 MethanesulfonicGlutaric N/A N/A 11.00 2.75 40 110 Acetic Poly N/A N/A 13.11 2.19phosphoric 41 110 Acetic Poly N/A N/A 13.99 1.75 phosphoric 42 75Trifluoroacetic Glutaric N/A N/A 10.00 5.00 43 75 MethanesulfonicGlutaric N/A N/A 9.63 4.81 44 75 Acetic Poly N/A N/A 13.13 2.19phosphoric 45 75 Acetic Propane N/A N/A 13.13 0.73 phosphonic 46 75Myristic Glutaric N/A N/A 4.25 2.13 47 150 Trifluoroacetic Glutaric N/AN/A 10.00 5.00 48 150 Methanesulfonic Glutaric N/A N/A 9.63 4.81 49 150Acetic Poly N/A N/A 13.13 2.19 phosphoric 50 150 Myristic Glutaric N/AN/A 4.25 2.13 51 150 Acetic Glutaric toluene 4.09 4.38 2.19 52 150Acetic Glutaric toluene 5.45 2.92 1.46 53 150 Acetic Glutaric toluene6.54 1.75 0.88 54 150 Myristic Glutaric toluene 4.09 2.13 1.06 55 150Myristic Glutaric toluene 5.45 1.42 0.71 56 150 Benzoic Glutaric toluene4.09 3.15 1.58 57 150 Benzoic Glutaric toluene 5.45 2.10 1.05 58 150Benzoic Glutaric toluene 6.54 1.26 0.63 59 150 Myristic GlutaricCyclohexanone 4.82 2.13 1.06 60 150 Myristic Glutaric Cyclohexanone 6.431.42 0.71 61 150 Benzoic Glutaric Cyclohexanone 4.82 3.15 1.58 62 150Benzoic Glutaric Cyclohexanone 6.43 2.10 1.05 63 150 Benzoic GlutaricCyclohexanone 7.72 1.26 0.63

TABLE 3 Anhydride Acid of the Acid (HX) of the Acid Anhydride ConversionAnhydride (X′₂O) Entry [X₂O] (M) [HX′] (M) (mol %) Conversion (mol %)  10.11 0.31  2.6%  7.0%  2 0.18 0.38  4.0%  8.7%  3 0.01 0.37  0.2%  9.3% 4 0.26 0.39  5.9%  9.0%  5 0.37 0.56  8.6% 12.7%  6 0.02 0.38  0.5% 9.7%  7 0.13 0.40  4.2% 12.6%  8 0.03 0.31  1.0% 11.6%  9 0.44 0.7310.0% 16.7% 10 0.36 0.54  8.3% 12.3% 11 0.02 0.41  0.6% 10.4% 12 0.120.49  3.9% 15.7% 13 0.09 0.35  3.2% 13.4% 14 0.04 N/D  0.9% N/D 15 0.07N/D  1.6% N/D 16 0.02 0.10  0.2%  4.7% 17 0.08 0.20  3.6%  9.0% 18 0.040.15  3.0% 10.0% 19 0.01 0.10  1.7% 11.1% 20 0.17 0.37  7.8% 16.7% 210.10 0.25  6.9% 16.8% 22 0.05 0.17  5.8% 19.5% 23 0.06 0.07  5.8% 11.9%24 0.03 0.18  2.0% 11.6% 25 0.01 0.14  0.7%  9.0% 26 1.37 2.21 31.3%50.5% 27 1.58 2.68 36.2% 61.2% 28 1.65 2.88 37.7% 65.9% 29 0.15 0.30 7.2% 14.3% 30 0.03 0.29  0.5%  5.8% 31 0.02 0.66  0.3% 13.6% 32 0.52N/D 11.9% N/D 33 0.03 0.31  0.5%  6.2% 34 0.03 0.68  0.5% 14.2% 35 0.55N/D 12.5% N/D 36 0.02 0.27  0.6%  5.4% 37 0.03 0.18  0.5%  7.3% 38 0.010.58  0.5%  9.7% 39 0.03 N/D  0.5% N/D 40 0.23 N/D  3.5% N/D 41 0.21 N/D 1.5% N/D 42 0.03 0.35  0.6% 6.9% 43 0.02 0.69  0.3% 14.4% 44 0.19 N/D 2.8% N/D 45 0.39 N/D  3.0% N/D 46 0.06 0.15  1.5%  7.0% 47 0.03 0.29 0.5%  5.8% 48 0.02 0.66  0.3% 13.6% 49 0.25 N/D  3.8% N/D 50 0.17 0.24 4.0% 11.1% 51 0.16 0.39  7.4% 17.9% 52 0.10 0.25  7.2% 17.1% 53 0.05N/D  5.1% N/D 54 0.13 0.22 12.4% 20.7% 55 0.05 0.09  3.8% 12.5% 56 0.140.22  4.3% 13.8% 57 0.04 0.15  3.4% 14.5% 58 0.02 0.09  2.8% 13.5% 590.08 0.20  7.1% 19.3% 60 0.05 0.15  3.5% 21.0% 61 0.06 0.27  2.0% 17.2%62 0.04 0.21  3.4% 20.3% 63 0.01 0.16  1.5% 25.2% N/D: not determined

EXAMPLE 4

This example demonstrates adding the organic mono-acid to theregenerable anhydride in stages in an embodiment of the invention.

To test the potential for multistage reactions, glutaric anhydride (10g) was heated in a 50-ml round-bottom flask to 100° C. Acetic acid (5.25g) was added, and the flask was sealed. After 1 hr, vacuum (10 torr(0.013 atm)) was applied for 15 min to most of the acetic acid andacetic anhydride, the system was repressurized to atmospheric pressure,and acetic acid was added again for another cycle. The results of thecycling experiment are shown in Table 4 and demonstrate that changingthe local concentrations of the material (e.g., in a reactivedistillation) results in higher yields than the equilibrium would allowin a single-stage batch process.

TABLE 4 Glutaric Anhydride Cycle Conversion (mol %) 1  5.8 2 10.1 3 14.04 17.2 5 20.0 6 23.1

All references, including publications, patent applications, andpatents, cited herein are hereby incorporated by reference to the sameextent as if each reference were individually and specifically indicatedto be incorporated by reference and were set forth in its entiretyherein.

The use of the terms “a” and “an” and “the” and “at least one” andsimilar referents in the context of describing the invention (especiallyin the context of the following claims) are to be construed to coverboth the singular and the plural, unless otherwise indicated herein orclearly contradicted by context. The use of the term “at least one”followed by a list of one or more items (for example, “at least one of Aand B”) is to be construed to mean one item selected from the listeditems (A or B) or any combination of two or more of the listed items (Aand B), unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. Recitation of ranges of valuesherein are merely intended to serve as a shorthand method of referringindividually to each separate value falling within the range, unlessotherwise indicated herein, and each separate value is incorporated intothe specification as if it were individually recited herein. All methodsdescribed herein can be performed in any suitable order unless otherwiseindicated herein or otherwise clearly contradicted by context. The useof any and all examples, or exemplary language (e.g., “such as”)provided herein, is intended merely to better illuminate the inventionand does not pose a limitation on the scope of the invention unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe invention.

Preferred embodiments of this invention are described herein, includingthe best mode known to the inventors for carrying out the invention.Variations of those preferred embodiments may become apparent to thoseof ordinary skill in the art upon reading the foregoing description. Theinventors expect skilled artisans to employ such variations asappropriate, and the inventors intend for the invention to be practicedotherwise than as specifically described herein. Accordingly, thisinvention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the invention unlessotherwise indicated herein or otherwise clearly contradicted by context.

The invention claimed is:
 1. A method of producing an anhydride of anorganic mono-acid comprising contacting an organic mono-acid andglutaric anhydride to produce the anhydride of the organic mono-acid anda diacid of the glutaric anhydride or a partially hydrolyzed glutaricanhydride.
 2. The method of claim 1, wherein the anhydride of theorganic mono-acid and the diacid of the glutaric anhydride or partiallyhydrolyzed glutaric anhydride are separated.
 3. The method of claim 2,wherein the separation step is by distillation.
 4. The method of claim2, wherein the separation step comprises forming a first streamcomprising the anhydride of the organic mono-acid and unreacted organicmono-acid and a second stream comprising the diacid of the glutaricanhydride or partially hydrolyzed glutaric anhydride and unreactedglutaric anhydride.
 5. The method of claim 4, wherein the unreactedorganic mono-acid is separated from the anhydride of the organicmono-acid.
 6. The method of claim 5, wherein the separated, unreactedorganic mono-acid is recycled.
 7. The method of claim 4, wherein thesecond stream is heated to regenerate the glutaric anhydride.
 8. Themethod of claim 7, wherein azeotropic distillation is used to regeneratethe glutaric anhydride.
 9. The method of claim 7, wherein the glutaricanhydride is recycled.
 10. The method of claim 1, wherein the organicmono-acid is a carboxylic acid.
 11. The method of claim 10, wherein thecarboxylic acid is a C₁₋₁₈ monocarboxylic acid.
 12. The method of claim11, wherein the C₁₋₁₈ monocarboxylic acid is selected from formic acid,acetic acid, propionic acid, butanoic acid, isobutyric acid, pentanoicacid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid,decanoic acid, undecanoic acid, dodecanoic acid, tridecanoic acid,tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoicacid, octadecanoic acid, and a combination thereof.
 13. The method ofclaim 1, wherein the organic mono-acid is acetic acid.
 14. The method ofclaim 1, wherein the anhydride of the monocarboxylic acid is aceticanhydride.
 15. The method of claim 1, wherein the organic mono-acid isadded in excess of the glutaric anhydride.
 16. The method of claim 1,wherein the organic mono-acid is added over multiple stages.
 17. Themethod of claim 1 further comprising adding a salt of the organicmono-acid.
 18. The method of claim 1 further comprising a solvent. 19.The method of claim 1 further comprising a catalyst.
 20. The method ofclaim 4, wherein the organic mono-acid is a carboxylic acid, and whereina portion of the carboxylic mono-acid is diverted to a vessel containingthe second stream.